Pit Road
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pit Road clear sky chart from 2005-11-06 to 2024-01-14.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	17% 10% 4 7% 6% 3 5% 5% 5% 6% 32%	74728
	Night	17% 11% 4 8% 6% 3 5% 4 5% 6% 31%	75028
Transparency	Day	52% 7% 11% 19% 10% 1	74433
	Night	53% 6% 11% 18% 10% 1	74857
Seeing	Day	22% 16% 30% 20% 9% 3	13285
	Night	22% 13% 30% 25% 9% 1	22563

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	15% 16% 7% 12% 10% 4 5% 4 3 5% 20%	1517
	11th to 20th	Day	19% 15% 7% 11% 7% 3 4 4 4 5% 22%	1464
	21st to end	Day	13% 14% 6% 11% 9% 4 5% 4 4 4 25%	1701
February	1st to 10th	Day	13% 14% 7% 13% 9% 4 5% 4 4 6% 20%	1620
	11th to 20th	Day	13% 14% 6% 10% 7% 4 4 5% 6% 6% 26%	1573
	21st to end	Day	18% 14% 4 9% 6% 5% 4 4 5% 6% 24%	1431
March	1st to 10th	Day	15% 13% 5% 9% 7% 4 6% 4 4 4 28%	1853
	11th to 20th	Day	14% 12% 6% 9% 8% 3 5% 4 3 5% 29%	1980
	21st to end	Day	18% 10% 4 6% 6% 3 3 3 4 6% 37%	2252
April	1st to 10th	Day	22% 13% 4 6% 5% 2 4 5% 4 6% 30%	2160
	11th to 20th	Day	21% 9% 3 6% 5% 3 3 4 4 5% 36%	2134
	21st to end	Day	23% 9% 3 7% 6% 3 3 3 4 6% 33%	2308
May	1st to 10th	Day	20% 8% 3 7% 6% 3 5% 3 5% 5% 36%	2520
	11th to 20th	Day	17% 8% 3 6% 7% 2 5% 5% 4 6% 37%	2478
	21st to end	Day	15% 7% 3 6% 6% 3 5% 6% 6% 7% 37%	2725
June	1st to 10th	Day	20% 8% 3 6% 7% 3 4 5% 6% 6% 31%	2520
	11th to 20th	Day	17% 5% 3 5% 5% 3 5% 5% 6% 7% 40%	2520
	21st to end	Day	17% 6% 3 6% 6% 4 6% 6% 6% 8% 33%	2520
July	1st to 10th	Day	11% 5% 3 5% 6% 3 6% 6% 6% 9% 39%	2520
	11th to 20th	Day	11% 5% 2 6% 6% 3 6% 6% 7% 8% 39%	2520
	21st to end	Day	11% 5% 3 6% 6% 3 5% 6% 7% 9% 39%	2744
August	1st to 10th	Day	11% 6% 3 7% 7% 4 6% 5% 6% 7% 38%	2412
	11th to 20th	Day	13% 6% 3 6% 6% 3 5% 6% 6% 8% 38%	2303
	21st to end	Day	14% 6% 3 5% 5% 3 5% 5% 8% 9% 36%	2404
September	1st to 10th	Day	14% 6% 3 6% 5% 3 5% 4 6% 8% 41%	2160
	11th to 20th	Day	14% 6% 2 5% 6% 4 4 4 5% 6% 44%	2160
	21st to end	Day	18% 7% 4 6% 5% 3 4 5% 6% 7% 36%	1899
October	1st to 10th	Day	21% 7% 3 7% 7% 3 5% 5% 3 6% 34%	1800
	11th to 20th	Day	23% 11% 4 8% 6% 2 5% 5% 5% 6% 26%	1800
	21st to end	Day	27% 11% 3 7% 7% 3 4 4 5% 6% 24%	1882
November	1st to 10th	Day	14% 12% 3 8% 5% 3 5% 4 4 7% 35%	1610
	11th to 20th	Day	18% 13% 5% 8% 7% 4 5% 5% 5% 6% 26%	1520
	21st to end	Day	21% 17% 5% 9% 7% 5% 5% 4 5% 4 17%	1520
December	1st to 10th	Day	20% 17% 7% 10% 9% 4 4 4 4 4 16%	1520
	11th to 20th	Day	20% 16% 5% 8% 7% 3 4 4 4 6% 21%	1906
	21st to end	Day	26% 19% 5% 13% 6% 2 2 2 3 3 18%	2772
January	1st to 10th	Night	16% 17% 8% 11% 9% 5% 5% 4 4 4 17%	2649
	11th to 20th	Night	18% 16% 5% 11% 8% 4 4 5% 4 4 22%	2569
	21st to end	Night	11% 15% 6% 10% 8% 4 5% 4 4 5% 28%	2653
February	1st to 10th	Night	13% 14% 7% 12% 10% 4 6% 5% 4 5% 21%	2340
	11th to 20th	Night	12% 14% 7% 11% 7% 4 5% 4 4 6% 26%	2273
	21st to end	Night	14% 13% 6% 9% 8% 3 4 4 5% 6% 28%	1824
March	1st to 10th	Night	17% 14% 6% 7% 7% 4 5% 3 5% 5% 29%	2092
	11th to 20th	Night	13% 15% 5% 7% 6% 3 4 4 4 6% 32%	1979
	21st to end	Night	16% 8% 4 8% 6% 3 3 4 5% 5% 38%	2103
April	1st to 10th	Night	20% 10% 5% 8% 6% 3 4 3 4 6% 32%	1800
	11th to 20th	Night	20% 10% 2 6% 5% 3 3 4 5% 6% 36%	1775
	21st to end	Night	21% 10% 3 8% 6% 3 4 3 5% 6% 31%	1665
May	1st to 10th	Night	20% 8% 3 5% 5% 3 4 3 4 8% 37%	1440
	11th to 20th	Night	20% 7% 2 4 5% 3 4 5% 4 7% 40%	1415
	21st to end	Night	12% 6% 2 5% 5% 3 5% 4 5% 8% 44%	1550
June	1st to 10th	Night	17% 6% 3 6% 6% 4 5% 5% 6% 8% 35%	1440
	11th to 20th	Night	14% 4 2 6% 5% 3 5% 5% 6% 7% 43%	1440
	21st to end	Night	17% 6% 3 5% 5% 4 5% 5% 7% 8% 35%	1440
July	1st to 10th	Night	11% 3 2 5% 5% 3 5% 6% 5% 8% 46%	1440
	11th to 20th	Night	12% 5% 3 5% 4 3 6% 5% 6% 9% 42%	1440
	21st to end	Night	8% 5% 2 6% 6% 3 6% 7% 7% 9% 42%	1574
August	1st to 10th	Night	10% 4 2 5% 7% 4 6% 6% 5% 8% 43%	1524
	11th to 20th	Night	10% 5% 2 6% 4 4 5% 5% 6% 8% 45%	1598
	21st to end	Night	11% 6% 2 5% 6% 3 5% 5% 5% 8% 44%	1934
September	1st to 10th	Night	11% 5% 3 7% 5% 3 4 5% 6% 6% 45%	1800
	11th to 20th	Night	16% 5% 2 5% 4 2 4 5% 5% 6% 48%	1800
	21st to end	Night	17% 6% 2 6% 5% 3 4 4 4 7% 42%	2057
October	1st to 10th	Night	21% 7% 3 5% 5% 3 5% 4 4 4 39%	2160
	11th to 20th	Night	21% 11% 3 7% 6% 3 6% 4 5% 5% 29%	2160
	21st to end	Night	24% 11% 4 7% 6% 3 5% 4 5% 5% 26%	2474
November	1st to 10th	Night	18% 12% 3 6% 5% 4 4 5% 5% 6% 33%	2468
	11th to 20th	Night	18% 12% 4 7% 7% 4 5% 5% 5% 6% 27%	2660
	21st to end	Night	21% 14% 5% 11% 6% 3 4 4 4 6% 21%	2660
December	1st to 10th	Night	21% 17% 7% 9% 8% 4 5% 4 4 4 17%	2660
	11th to 20th	Night	19% 17% 6% 9% 6% 3 4 4 3 4 25%	3288
	21st to end	Night	27% 18% 6% 12% 6% 3 3 3 3 3 16%	4884

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	68% 6% 8% 13% 5%	1518
	11th to 20th	Day	66% 5% 8% 10% 9% 1	1464
	21st to end	Day	64% 5% 8% 12% 9% 2	1701
February	1st to 10th	Day	65% 7% 8% 15% 4 1	1620
	11th to 20th	Day	58% 6% 13% 14% 8% 1	1582
	21st to end	Day	61% 5% 11% 13% 9% 1	1431
March	1st to 10th	Day	59% 5% 8% 17% 10% 1	1856
	11th to 20th	Day	57% 5% 11% 15% 10% 2	1980
	21st to end	Day	49% 4 9% 19% 13% 6%	2252
April	1st to 10th	Day	56% 4 8% 18% 11% 3	2160
	11th to 20th	Day	50% 4 8% 22% 14% 2	2134
	21st to end	Day	53% 5% 8% 15% 16% 4	2308
May	1st to 10th	Day	49% 5% 9% 18% 14% 4	2520
	11th to 20th	Day	47% 6% 8% 20% 17% 2	2482
	21st to end	Day	44% 7% 12% 21% 13% 4	2725
June	1st to 10th	Day	52% 8% 9% 19% 11% 1	2520
	11th to 20th	Day	42% 8% 11% 22% 14% 2	2520
	21st to end	Day	47% 8% 12% 21% 12% 1	2520
July	1st to 10th	Day	37% 9% 12% 26% 14% 1	2450
	11th to 20th	Day	38% 9% 15% 25% 12%	2445
	21st to end	Day	40% 10% 14% 27% 10%	2591
August	1st to 10th	Day	44% 8% 14% 22% 11% 1	2398
	11th to 20th	Day	42% 8% 17% 25% 8% 1	2303
	21st to end	Day	41% 9% 16% 24% 10% 1	2404
September	1st to 10th	Day	39% 8% 14% 26% 11%	2160
	11th to 20th	Day	40% 6% 12% 31% 11% 1	2160
	21st to end	Day	47% 6% 15% 24% 8%	1899
October	1st to 10th	Day	51% 7% 10% 20% 11% 1	1800
	11th to 20th	Day	59% 7% 14% 16% 5% 1	1800
	21st to end	Day	61% 6% 12% 15% 5% 1	1882
November	1st to 10th	Day	50% 6% 15% 22% 7% 1	1610
	11th to 20th	Day	58% 7% 14% 13% 7% 1	1520
	21st to end	Day	68% 7% 11% 9% 5% 1	1520
December	1st to 10th	Day	72% 6% 10% 9% 3	1520
	11th to 20th	Day	63% 8% 10% 12% 7%	1906
	21st to end	Day	74% 3 7% 14% 2	2772
January	1st to 10th	Night	70% 6% 10% 9% 4	2649
	11th to 20th	Night	66% 6% 9% 11% 7% 1	2569
	21st to end	Night	58% 5% 9% 17% 10%	2653
February	1st to 10th	Night	65% 5% 10% 13% 6% 1	2340
	11th to 20th	Night	59% 5% 12% 17% 7% 1	2275
	21st to end	Night	56% 6% 10% 18% 9% 1	1824
March	1st to 10th	Night	58% 5% 10% 16% 9% 1	2102
	11th to 20th	Night	52% 5% 13% 17% 12% 2	1980
	21st to end	Night	48% 6% 8% 20% 14% 4	2103
April	1st to 10th	Night	55% 4 9% 18% 12% 2	1800
	11th to 20th	Night	49% 5% 8% 22% 14% 2	1775
	21st to end	Night	54% 4 8% 15% 16% 2	1665
May	1st to 10th	Night	48% 5% 8% 19% 16% 4	1440
	11th to 20th	Night	44% 5% 8% 23% 17% 3	1416
	21st to end	Night	38% 7% 15% 20% 17% 3	1551
June	1st to 10th	Night	45% 8% 14% 23% 9% 1	1440
	11th to 20th	Night	38% 8% 11% 24% 16% 2	1440
	21st to end	Night	44% 7% 15% 21% 13% 1	1440
July	1st to 10th	Night	32% 10% 14% 23% 19% 2	1400
	11th to 20th	Night	38% 7% 13% 29% 13%	1392
	21st to end	Night	35% 9% 16% 28% 12%	1486
August	1st to 10th	Night	38% 9% 16% 24% 13%	1514
	11th to 20th	Night	34% 10% 18% 27% 12% 1	1598
	21st to end	Night	37% 7% 15% 29% 11% 1	1934
September	1st to 10th	Night	38% 8% 13% 27% 14% 1	1800
	11th to 20th	Night	36% 7% 15% 32% 9% 1	1800
	21st to end	Night	42% 7% 14% 29% 8%	2057
October	1st to 10th	Night	47% 6% 12% 21% 14%	2160
	11th to 20th	Night	55% 8% 12% 18% 7%	2160
	21st to end	Night	59% 7% 12% 14% 8%	2474
November	1st to 10th	Night	51% 6% 15% 19% 9%	2468
	11th to 20th	Night	57% 8% 13% 15% 7% 1	2660
	21st to end	Night	65% 6% 13% 13% 3	2660
December	1st to 10th	Night	70% 7% 9% 11% 4	2660
	11th to 20th	Night	64% 6% 10% 14% 7% 1	3288
	21st to end	Night	75% 4 7% 11% 3	4884

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	19% 22% 33% 22% 3 1	180
	11th to 20th	Day	30% 16% 37% 13% 4 1	166
	21st to end	Day	24% 18% 35% 15% 7%	228
February	1st to 10th	Day	25% 28% 33% 12% 3	240
	11th to 20th	Day	25% 28% 39% 8% 1	240
	21st to end	Day	33% 23% 32% 12% 1	297
March	1st to 10th	Day	26% 20% 34% 16% 3	420
	11th to 20th	Day	26% 20% 33% 17% 4	420
	21st to end	Day	30% 19% 30% 14% 6%	462
April	1st to 10th	Day	30% 20% 27% 16% 6%	420
	11th to 20th	Day	32% 19% 21% 17% 9% 2	412
	21st to end	Day	32% 17% 31% 14% 5% 2	420
May	1st to 10th	Day	27% 15% 28% 20% 8% 2	423
	11th to 20th	Day	19% 19% 32% 19% 9% 3	447
	21st to end	Day	17% 17% 33% 21% 10% 3	485
June	1st to 10th	Day	23% 15% 32% 21% 8% 1	450
	11th to 20th	Day	18% 15% 27% 24% 13% 3	450
	21st to end	Day	17% 13% 32% 23% 12% 3	450
July	1st to 10th	Day	11% 7% 33% 34% 13% 3	445
	11th to 20th	Day	10% 11% 33% 27% 15% 3	444
	21st to end	Day	12% 8% 34% 29% 13% 3	488
August	1st to 10th	Day	13% 7% 30% 30% 14% 6%	446
	11th to 20th	Day	14% 6% 27% 28% 16% 8%	439
	21st to end	Day	14% 12% 29% 24% 15% 7%	495
September	1st to 10th	Day	14% 12% 29% 21% 15% 8%	450
	11th to 20th	Day	16% 12% 23% 24% 16% 10%	450
	21st to end	Day	16% 14% 29% 22% 13% 6%	450
October	1st to 10th	Day	26% 15% 22% 20% 14% 3	450
	11th to 20th	Day	28% 21% 31% 12% 7% 1	450
	21st to end	Day	30% 17% 28% 19% 4 1	446
November	1st to 10th	Day	25% 18% 32% 18% 6% 1	304
	11th to 20th	Day	26% 27% 30% 11% 6% 1	180
	21st to end	Day	31% 22% 34% 8% 3 2	180
December	1st to 10th	Day	29% 14% 39% 14% 4	180
	11th to 20th	Day	28% 27% 32% 11% 2 1	180
	21st to end	Day	28% 23% 30% 15% 3 2	198
January	1st to 10th	Night	25% 19% 33% 19% 4	760
	11th to 20th	Night	29% 15% 28% 21% 6%	735
	21st to end	Night	17% 14% 36% 26% 6% 1	792
February	1st to 10th	Night	20% 18% 40% 19% 3	720
	11th to 20th	Night	21% 17% 39% 19% 4	703
	21st to end	Night	21% 20% 31% 25% 3	592
March	1st to 10th	Night	26% 17% 33% 21% 3	720
	11th to 20th	Night	23% 20% 31% 20% 6%	720
	21st to end	Night	22% 15% 33% 23% 8%	792
April	1st to 10th	Night	26% 15% 32% 22% 5%	720
	11th to 20th	Night	25% 17% 29% 22% 7%	711
	21st to end	Night	24% 14% 27% 25% 9% 1	585
May	1st to 10th	Night	24% 7% 29% 29% 10% 1	360
	11th to 20th	Night	21% 12% 30% 30% 6%	354
	21st to end	Night	15% 7% 38% 30% 10% 1	389
June	1st to 10th	Night	18% 8% 33% 34% 7% 1	360
	11th to 20th	Night	14% 10% 32% 32% 12%	360
	21st to end	Night	20% 8% 28% 30% 14%	360
July	1st to 10th	Night	10% 4 33% 37% 14% 1	350
	11th to 20th	Night	13% 5% 26% 41% 15%	348
	21st to end	Night	9% 4 32% 41% 13% 1	394
August	1st to 10th	Night	10% 4 25% 38% 21% 1	450
	11th to 20th	Night	11% 2 23% 39% 21% 4	534
	21st to end	Night	13% 8% 28% 32% 18% 2	746
September	1st to 10th	Night	13% 7% 30% 29% 19% 2	720
	11th to 20th	Night	19% 7% 21% 31% 19% 3	720
	21st to end	Night	20% 11% 22% 27% 19% 2	720
October	1st to 10th	Night	25% 8% 29% 24% 13% 1	720
	11th to 20th	Night	27% 13% 32% 18% 9% 1	720
	21st to end	Night	30% 14% 27% 23% 5%	792
November	1st to 10th	Night	25% 15% 28% 24% 7% 1	740
	11th to 20th	Night	25% 18% 31% 16% 10% 1	760
	21st to end	Night	30% 17% 26% 23% 5%	760
December	1st to 10th	Night	30% 18% 31% 16% 5%	760
	11th to 20th	Night	27% 18% 31% 20% 4 1	760
	21st to end	Night	32% 16% 29% 20% 3 1	836

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